1. Field of the Invention
The present invention relates to gas flow control devices, and more particularly to pressure regulators that are suitable for use in service with highly pure and highly corrosive gases.
2. Description of Related Art
The demands on gas delivery systems in the semiconductor fabrication industry have made the design of gas flow control devices in general, and of pressure regulators in particular, especially challenging. The gases used must be of ultrahigh purity in order to avoid contamination of the devices undergoing fabrication. At the same time, the gases commonly used in semiconductor fabrication are highly corrosive, thus requiring the wetted surfaces, i.e., surfaces that will contact the flowing gases, to be made of expensive corrosion-resistant metals, such as stainless steel, and to be highly polished or otherwise treated to achieve the necessary degree of smoothness to substantially prevent erosion-corrosion of the metal surface. As used herein, the term polished is intended to refer to any process or treatment for increasing the smoothness of a surface, and is not limited to specific polishing techniques, such as mechanical polishing. In addition, the term polished may also refer to the state of smoothness of the internal surface of an as-drawn section of tubing, if the drawing process is conducted so as to yield a very smooth surface.
Furthermore, current designs necessitate the use of intersecting bores within the device body, in order to achieve the correct flow of gases. The resultant internal angles, in the form of internal tees and elbows, provide sources for increased contamination in a high-purity and/or corrosive gas stream. The proposed design eliminates these internal angular passages, thereby reducing the possibilities of contaminating the gases flowing through the device.
In addition, while threaded connections between the body of the regulator and the inlet, outlet, and gauge connectors or fittings are generally preferred for economy of manufacture and assembly, in this high purity, high corrosivity gas service, it is desirable, where possible, to avoid having threaded connections exposed to the gas stream. This has led in the past to fabricating the regulator body from barstock of expensive, corrosion-resistant materials, wherein the regulator body is machined and drilled to form the necessary passages. The passages must then be polished to achieve the necessary smooth finish as discussed above, and the connectors, generally VCR.RTM. or other brands of metal-to-metal face seal connectors, are butt welded to the regulator body. VCR.RTM. is a registered trademark of Swagelok Co., for connectors or couplings of the type used in ultrahigh purity gas service.
These regulator designs, while providing good performance in their use in semiconductor fabrication gas service, are expensive to manufacture, and have other disadvantages including the inherent inflexibility of the solid barstock body design in configuring or orienting the inlets and/or outlets in different positions, or in altering what is referred to as the face-to-face dimension, to accommodate different end uses or end users' preferences.
Other gas flow control devices, such as diaphragm valves and flow meters, are also difficult and expensive to manufacture for use with high purity and/or highly corrosive gases, particularly in providing the smoothest possible surfaces for the gas flow passages.
It is therefore a principal object of the present invention to provide a gas flow control device, and, in particular, a pressure regulator that will provide all of the desirable features of the existing regulators in use in high purity, high corrosivity gas service.
It is a further principal object of the present invention to provide a pressure regulator that will have design flexibilities not attainable in the solid barstock body regulators presently used in the high purity, high corrosivity gas service.
It is a further important object of the present invention to provide a pressure regulator for use in high purity and/or high corrosivity gas service that has no threaded connections exposed to the gas stream, and avoids the use of gaskets in making the seals and connections.
Further important objects of the present invention are to provide a pressure regulator for use in high purity, highly corrosive gas service that has a low dead volume, and one which allows for simple maintenance and repair of the regulator. Dead volume is internal volume that has little or no fluid circulation through it.